Asymmetric Screw Thread Profile for Self-Locking Fastening
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Solution Overview
Problem
Existing screws often experience insufficient adhesion during unscrewing, leading to loose connections, despite design modifications aimed at improving thread engagement.
Innovation Solution
A screw design featuring threads with two different angles between the longitudinal axis and the flanks, where the angle in the thread valley is shallower than at the thread ridge, enhancing adhesion and preventing loosening through optimized stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional thread designs with uniform flank angles are used, then the screw can be easily manufactured, but the adhesion counter to unscrewing is insufficient leading to loose connections
Solution Approach 1:
The thread flanks are designed with different angles in different regions: the first flank has a first angle and the second flank has a second angle that is different from the first angle. This local differentiation of geometric properties optimizes the adhesion counter to unscrewing in specific regions while maintaining manufacturability.
Solution Approach 2:
The thread profile employs asymmetric flank angles where the two flanks of the thread have different angles relative to the thread axis. This asymmetry creates unequal normal forces on the two flanks, generating an adhesion counter moment that prevents loosening during unscrewing operations.
2Reliability
If thread flanks with equal angles are used, then the manufacturing process is simple, but the adhesion counter to unscrewing is insufficient causing the connection to loosen
Solution Approach 1:
The thread structure incorporates local quality variation by assigning different angles to the first and second flanks. The first flank angle and second flank angle are specifically optimized to maximize adhesion counter to unscrewing, while the thread geometry remains compatible with standard manufacturing processes.
Solution Approach 2:
The thread design changes the geometric parameters of the thread flanks by specifying different angles for the first and second flanks. This parameter differentiation directly increases the adhesion counter to unscrewing by creating an asymmetric force distribution that generates a locking moment.
3Reliability
If conventional thread profiles are used, then the screw design is simple, but the connection loosens due to insufficient friction-based adhesion
Solution Approach 1:
The thread profile features asymmetric flanks with different angles relative to the thread axis. This asymmetry creates a mechanical advantage where the normal forces on the two flanks are unequal, generating a self-locking effect that resists loosening without requiring additional locking mechanisms.
Solution Approach 2:
Different regions of the thread profile have optimized local geometric properties. The first flank and second flank have specifically designed angles that maximize the adhesion counter to unscrewing in their respective positions, creating a localized locking effect at the thread-mating part interface.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The screw design facilitates easy screwing and self-locking, providing a stable connection by improving adhesion and reducing the likelihood of loosening.
Implementation Method 1
By screwing in the screw, a force N is created acting in the normal direction between the mutually facing flank surfaces, and as a consequence of the friction between the two, an adhesion counter to the rotation is created.
Data Source
AI summary
A screw (1) is proposed, which has a shank (4) having a longitudinal axis (12), which has a first end (9) and a second end (17), the shank (4) having at least one thread (5) at least to some extent, the thread (5) having a thread groove (6), which has a thread ridge (7), a thread valley (8), a thread depth resulting from the thread ridge (7) and the thread valley (8), a flank (10) facing the first end (9) of the shank (2) and a flank (11) facing away from the first end (9) of the shank (2), a flank (10), from the thread valley to the thread ridge (7), facing the first end (9) of the shank (2) having at least two different angles enclosed between the longitudinal axis (12) and the flank (10) and/or a flank (11), from the thread valley (8) to the thread ridge (7), facing away from the first end (9) of the shank (2) having at least two different angles enclosed between the longitudinal axis (12) and the flank (11), the angle (20) enclosed in the thread valley (8) of a flank (10) facing the first end (9) of the shank (2) being shallower than the angle (21) enclosed at the thread ridge (7), and/or the angle (22) enclosed in the thread valley (8) of a flank (11) facing away from the first end (9) of the shank (2) being shallower than the angle (23) enclosed at the thread ridge (7), as a result of which, easy screwing of the screw (1) according to the invention into a mating part becomes possible and self-locking prevents loosening of the screw (1) according to the invention.